High demands are made on the supply of electric components with electric energy, and here particularly on the supply of semiconducting chips. An important demand is to perform the energy supply in polarity-inversion-protected manner. Within the scope of the present application, by “polarity-inversion-protected supply” of an electric component or of a chip, a supply with electric voltage is understood, in which the input resistance at a terminal designed for a positive voltage for example becomes sufficiently high-ohmic when applying a negative voltage, so that the resulting current flow does not lead to thermal overload. Moreover, all elements also need to have the required voltage strength.
A first possible embodiment of a polarity-inversion-protected supply of an electric component is to connect a diode or a transistor connected as a diode between an external supply voltage Vsup,ext and a regulation circuit providing an internal regulated supply voltage Vsup,int, so that the diode is operated in pass direction when a positive supply voltage Vsup,ext is applied, and in blocking direction in the case of a negative external supply voltage Vsup,ext. Here, within the scope of the present application, in the case of transistors, an emitter terminal of a bipolar transistor or a source terminal of a field-effect transistor is understood by a source terminal, a collector terminal of a bipolar transistor and a drain terminal of a field-effect transistor by a sink terminal, as well as a base terminal of a bipolar transistor and a control terminal or gate terminal of a field-effect transistor by a control terminal.
FIG. 2 shows such a circuit of a possible realization of a polarity-inversion-protected supply of an electric component. FIG. 2 shows a series connection of a pnp bipolar transistor 800 and an npn bipolar transistor 810, which are connected to the external supply voltage Vsup,ext with an emitter terminal of the pnp bipolar transistor 800 and to a regulated internal supply voltage Vsup,int with an emitter terminal of the npn bipolar transistor 810. A collector terminal of the pnp bipolar transistor 800 is connected to a collector terminal of the npn bipolar transistor 810 and a base terminal of the pnp bipolar transistor 800.
A base terminal of the npn bipolar transistor 810 is connected to a regulating means not included in FIG. 2. The regulating means not shown in FIG. 2 regulates the internal, regulated supply voltage Vsup,int from a voltage VnetX present at the collector terminal of the npn bipolar transistor 810. The regulating means is not shown in FIG. 2, since it is not subject matter of the present application, but rather known.
The npn bipolar transistor 810, via which the actual regulation of the internal regulated supply voltage Vsup,int is done, is, however, not polarity-inversion-protected with reference to a positive external supply voltage Vsup,ext. This is due to the fact that, especially with integrated circuits constructed on a semiconductor substrate doped with holes (p substrate), the diode formed between collector and substrate is operated in pass direction and destroyed due to the high voltage present and the current flow resulting therefrom, when applying a great-magnitude negative voltage (e.g. −20 V) to the area doped with electrons, which forms the collector of the npn bipolar transistor 810 (n collector).
In other words, if the intermediate voltage Vsup,ext (e.g. 3 V . . . 30 V) is applied to the IC (integrated circuit), the IC generates an internal, regulated voltage Vsup,int (e.g. 2.5 V), by suitably regulating the base of the npn bipolar transistor 810 (not shown, since prior art). Here, the npn bipolar transistor 810 functions as a series regulator (pass transistor). The collector of the npn bipolar transistor 810 is, however, not polarity-inversion-protected: i.e., when applying a voltage negative as opposed to the p substrate lying at ground potential or at a reference potential (e.g. −20 V), the collector-substrate diode opens, draws a lot of current and is destroyed.
A possible polarity inversion protection is to connect a diode or a pnp bipolar transistor 800 connected as a diode, as FIG. 2 shows, between the external supply potential Vsup,ext and the collector terminal of the npn bipolar transistor 810. A connection of a pnp bipolar transistor, as shown by FIG. 2 for the pnp bipolar transistor 800, in which the base terminal and the collector terminal are connected or shorted by a low-ohmic line, is also referred to as a transistor diode. In case of a polarity inversion, a voltage negative as opposed to the reference potential is present at the area doped with holes of the semiconducting substrate, which forms the emitter of the pnp bipolar transistor 800, so that the pnp bipolar transistor 800 blocks.
In other words, the above described opening of the collector-substrate diode, drawing a large current, and the destruction of the npn bipolar transistor 810, which will also be referred to as regulating transistor in the following, is prevented in the prior art by laying a pnp transistor 800 connected as a diode between the collector of the npn bipolar transistor and the external supply pin. Thus, the p emitter of the pnp bipolar transistor 800, which blocks at a negative potential as opposed to the substrate (negative voltage at p), is located at an external supply pin.
The disadvantage of this solution is that the transistor diode 800 requires at least a potential difference of a flow voltage between its emitter terminal and its collector terminal, so as to become conducting. Within the scope of the present application, by a flow voltage, a potential difference between an anode terminal and a cathode terminal of a diode or between a base and an emitter terminal of a bipolar transistor is understood, which leads to a current flow through the diode or to a collector current through the bipolar transistor of 1 mA, wherein the diode and the bipolar transistor are operated in pass direction. A flow voltage thus corresponds to about the voltage at which a bend occurs in case of a diode characteristic curve or the transmission characteristic curve of a bipolar transistor.
In case of a diode or a transistor diode based on silicon, a flow voltage thus typically ranges from about 500 mV to 800 mV. Since a voltage between 20 mV and 250 mV, which is also referred to as saturation voltage and corresponds to the output characteristic curve field of a typical bipolar transistor of the collector-emitter voltage at which the output characteristic curves have a bend, also typically drops in a bipolar transistor across the path between a collector terminal and an emitter terminal at a collector current of 1 mA, the circuit in FIG. 2 requires an external supply voltage Vsup,ext exceeding at least the internal, regulated supply voltage Vsup,int by the sum of a flow voltage and a saturation voltage. This means that the external supply voltage Vsup,ext has to be greater than 3.5 V, for example, at an internal, regulated supply voltage Vsup,int of about 2.5 V.
In other words, the disadvantage of the circuit shown in FIG. 2 is that the diode 800 requires at least a flow voltage so as to become conducting. This means, when for example Vsup,int is regulated to 2.5 V, the circuit only functions for external supply voltages Vsup,ext of about 3.5 V and above at low temperatures, because then the base-emitter voltage of the bipolar transistor 800 becomes about 0.9 V and the npn bipolar transistor 810 still needs at least 0.1 V saturation voltage so as to be able to work.
A further procedure to realize a possible polarity inversion protection is the so-called “low-drop” technology. Here, the regulation of the internal, regulated supply voltage Vsup,int from the external supply voltage Vsup,ext is no longer done via an npn bipolar transistor, as it is shown in FIG. 2, but a pnp bipolar transistor is rather used also for the regulation of the internal supply voltage Vsup,int. In other words, the npn emitter follower may of course be omitted and constitute a series regulator solely with a pnp bipolar transistor. This procedure solves the problem of the flow voltage occurring in addition, as it occurs in an additional series-connected diode or transistor diode. In this case, the circuit functions as long as the external supply voltage Vsup,ext exceeds the internal, regulated supply voltage Vsup,int by at least the saturation voltage, i.e. typically between 20 and 250 mV.
In other words, this procedure solves the problem of the drop voltage: The circuit functions as long as the external supply voltage Vsup,ext is greater than the sum of the regulated, internal supply voltage Vsup,int and about 100 mV. The disadvantage of this solution is that the internal, regulated supply voltage Vsup,int now lies at a collector of a pnp bipolar transistor, which is substantially more high-ohmic than the emitter of the npn bipolar transistor 810 in FIG. 2. The reason for the higher internal resistance of the collector than that of the emitter is that the former constitutes a current source, but the latter a voltage source, and lies in the slope of the Ice-Uce output characteristic curve (output characteristic curve Ice versus Uce) as well as the Ie-Ube input characteristic curve (input characteristic curve Ie versus Ube). Thereby, it becomes much more difficult to keep the locked loop of the internal, regulated supply voltage Vsup,int stable, particularly when the capacitive load at Vsup,int has not exactly been determined yet. So as to guarantee the regulation of the internal, regulated supply voltage Vsup,int in this case, the internal, regulated supply voltage Vsup,int has to be loaded to the reference potential or also to ground via a stabilizing load or also a shunt path. The current flowing off through the stabilizing load is used for stabilizing the regulating circuit and thus reduces the current efficiency of such a current regulation, wherein the current efficiency is defined as the ratio of the current the regulation gives off to the actual load connected thereto divided by the overall current consumption, i.e. including the own current consumption of the regulation.
In other words, a relatively large current (as compared with the overall current need of the circuit) has to be sunk from Vsup,int via a shunt path or stabilizing load to ground, in order to keep the locked loop stable. This current is used for achieving the stability and wastes and reduces the efficiency of such a voltage regulation: For example, if Vsup,int is loaded with 5 mA, about 1.7 mA additional current is needed in order to keep the low-drop regulator stable. Its efficiency thus is about 75%, whereas the efficiency of the emitter follower shown in FIG. 2 is far higher at about 90%.
FIG. 3 shows an example for such a low-drop circuit. A pnp bipolar transistor 820 is connected to the external supply voltage Vsup,ext with an emitter terminal and to the regulated, internal supply voltage Vsup,int with a collector terminal. A base terminal of the pnp bipolar transistor 820 is connected to a regulating unit not included in FIG. 3 since it is known and does not represent the subject matter of the present application. Moreover, FIG. 3 shows an NMOS transistor 830 connected between the regulated, internal supply voltage Vsup,int and a reference potential.
The pnp bipolar transistor 820 here serves for the regulation of the internal supply voltage Vsup,int. The NMOS transistor 830 serves for loading the regulated, internal supply voltage Vsup,int and thus represents the stability load explained further above. Alternatively, instead of the NMOS transistor 830, also a PMOS transistor may be used as stability load. The advantage of this solution is that again a low-ohmic source terminal lies at the terminal for Vsup,int, and not a high-ohmic drain terminal.